Definition of diffraction

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Photonics Dictionary

diffraction

Diffraction is a fundamental wave phenomenon that occurs when a wave encounters an obstacle or aperture, causing the wave to bend around the edges and spread out. This effect is most commonly observed with light waves, but it can also occur with other types of waves, such as sound waves, water waves, and even matter waves in quantum mechanics.

Wave interaction: Diffraction occurs when a wave encounters an obstacle (e.g., an edge or slit) or a series of obstacles, such as a diffraction grating. The wave interacts with these obstacles, causing the wave to change direction and spread out.

Huygens' principle: This principle explains diffraction by stating that each point on a wavefront acts as a source of secondary spherical wavelets. As these wavelets propagate, they interfere with each other, leading to the bending and spreading of the wave.

Single-slit diffraction: When a wave passes through a single narrow slit, it spreads out on the other side, forming a pattern of alternating bright and dark fringes. The central maximum is the brightest and widest, with successive maxima decreasing in intensity.

Double-slit diffraction: When a wave passes through two closely spaced slits, the wavefronts emerging from each slit interfere with each other, creating an interference pattern of bright and dark fringes on a screen. This experiment famously demonstrates the wave nature of light.

Diffraction gratings: A diffraction grating consists of many closely spaced slits or grooves. When light passes through or reflects off a grating, it produces multiple diffraction orders, resulting in a spectrum of colors. This property is widely used in spectroscopy.

Applications:

Optics: Diffraction is used in optical instruments such as spectrometers, microscopes, and cameras to analyze light properties.

Acoustics: Understanding diffraction helps in designing auditoriums and concert halls to control sound distribution.

X-Ray crystallography: X-ray diffraction is used to determine the atomic structure of crystals.

Quantum mechanics: Diffraction experiments with particles such as electrons demonstrate the wave-particle duality of matter.

Mathematical description: Diffraction patterns can be mathematically described using the wave equation and principles of superposition. The intensity of the diffraction pattern can be calculated using equations such as the Fraunhofer and Fresnel diffraction equations, depending on the distance from the diffracting object.

Examples of diffraction:

Light: The fringes of light and dark bands observed when light passes through a narrow slit or around a small object.

Sound: The ability to hear sound waves around obstacles, such as hearing someone speaking from around a corner.

Water waves: The bending and spreading of water waves as they pass through an opening in a barrier or around an object in the water.

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diffraction

Presented by Keith Tripp, Three Rivers Community College